The invention concerns a module support structure for printed circuit boards which can be inserted on guide rails, having two parallel side walls and at least four parallel module rails to which the guide rails can be mounted. The module rails comprise a cylindrical hole at each end for accepting a mounting bolt and the side walls have mounting holes for the mounting bolts and projections for positioning the module rails.
An exact guiding of the printed circuit board in the guide rails of a module support structure is clearly imperative, in particular for electronics applications in which multi-poled plugs of the smallest dimensions are used. The precise alignment of the guide rails depends, however, definitively on the precise, in particular vertical, positioning of the module rails on the side walls of the module support structure.
The side walls of conventional module support structures have inwardly directed projections, disposed at a particular separation above or below the mounting holes for the module rails. These projections function as positioning aids when mounting the module rails to the side walls. The module rails are positioned on the projections and the mounting bolts are then passed through the mounting holes of the side walls into the cylindrical holes of the module rails provided therefor.
For assembly or manufacturing purposes, the mounting holes in the side walls have an inner diameter which is significantly larger than the outer diameter of the mounting bolts. A displacement of the module rails perpendicular to the screw axis is therefore possible even when the mounting bolt seats in the mounting hole.
Problems thereby result, since the manual dexterity of the individual assembler determines whether or not the module rails actually seat on the corresponding projections after tightening the mounting bolts. Moreover, the module rails tend to rotate along with the mounting bolts when same are tightened.
As a result, in accordance with the described prior art, the close assembly tolerances necessary for the positioning of the guide rails for various applications can not be achieved or can only be achieved with an unacceptable degree of manual difficulty.
In order to achieve a restricted guidance seating of the module rails on the projections when tightening the mounting bolts, it has also been proposed that the mounting holes be countersunk in the outer side of the side walls and that beveled head bolts be used as mounting bolts.
However, this approach also has problems since, in this case as well, the inside diameter of the mounting holes is larger than the outer diameter of the threaded shaft of the mounting bolts. Consequently, the beveled head of a mounting bolt does not seat in the countersunk mounting hole at all sides, rather only at an upper section thereof, when the module rail is positioned on the projection. The frictional connection between the mounting bolts and the side wall is therefore unsatisfactory and causes concern that fatigue effects occur after longer periods of time. Moreover, the countersinking of the mounting holes in the side walls is very difficult from a manufacturing point of view.